Tropical Fish Keeping - Aquarium fish care and resources

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wildman 04-25-2008 11:20 AM

Newbie--which bulb?
Hi, I have a 29Gal. tank with a standard hood and a choice of 2 bulbs -a Hagen Power-Glo T-8 20watt 18000k bulb, or a marineland eclipse natural daylight F18T8 Hg bulb.

Which will give me better light for plants and higher intensity?

I have tried searching for these bulbs online w/ little success. I have also tried online articles but just get confused. I think that I probably have low to moderate lighting--am I right?

My substrate is Flourite black, for what it is worth.

herefishy 04-25-2008 11:28 AM

The 18000K is too hot. Look for a bulb in the 6700K-10000k range. You did not say what plants you were keeping, but most hobbyists do well lights in this range.

wildman 04-25-2008 06:09 PM

too hot???
What do you mean by "too hot?" Will it give my fish/ shrimp/ plants "sun burn?" I had a cherry shrimp that just went belly up less than 24 hours after I bought it.

herefishy 04-26-2008 01:56 AM

By too hot< I meant that you had too much light. Kelvins( the "K") is defined as he basic unit of luminous intensity equal to 1/60 of the luminous intensity per square centimeter of a black body radiating at the temperature of 2,046 degrees Kelvin.

Now that I've thoroughly confused you, it is a means to measure light by using the starting point of absolute zero, a theoretical point at which all energy ceases and is no longer emitted. Some have said that it si based on the temperature of the sun as being a maximum. I do not find that to be true. Plants do best at Kelvin ratings beginning around 6700K or just slightly lower and progressing to around 12000K or so. There are some plants that enjoy light around 15000K-18000K but those are few.

Depending on the species of plant you intend to keep, I feel confident that a bulb in the 6700K to 8500K would be sufficient, unless your tank is over 30" deep(top to bottom). Multiple bulbs may be needed to provided sufficient footcandles to the bottom of the tank. I have found it necessary, at times, to use more than a single bulb. In my plant tanks in my fishroom, I am currently using (2)4' 8400K bulbs at no more than 26" above the substrate of any one tank. This puts the plants that I have in the medium light range. Not to say that I don't have low light plants in those tanks, because I do. All lights are on timers interphased to CO2 injection. All kind of trick, but these plants are for profit. Not all tanks are using CO2, but a few are.

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